The optimization of modal sound attenuation in ducts, in the absence of mean flow

Tester, Brian J.

doi:10.1016/s0022-460x(73)80358-x

Cited by 114 publications

(50 citation statements)

References 7 publications

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“…The aim of this paper, is i) to illustrate the potentialities of periodic rigid inclusions embedded in a porous material for waveguide attenuation and ii) to link the optimal modal attenuation with higher modes interaction such as double roots of the dispersion equation [25][26][27] or exceptional points [28][29][30][31][32][33][34][35] . The interest of such configurations has been shown in a preliminary numerical work 36 for basic 2D inclusions.…”

Section: Introductionmentioning

confidence: 99%

Sound attenuation optimization using metaporous materials tuned on exceptional points

Xiong¹,

Nennig²,

Aurégan³

et al. 2017

The Journal of the Acoustical Society of America

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A metamaterial composed of a set of periodic rigid resonant inclusions embedded in a porous lining is investigated to enhance the sound attenuation in an acoustic duct at low frequencies. A transmission loss peak is observed on the measurements and corresponds to the crossing of the lower two Bloch modes of an infinite periodic material. Numerical parametric studies show that the optimum modal attenuation can be achieved at the exceptional point in the parameter plane of inclusion position and frequency, where the two lower modes merge.

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Section: Introductionmentioning

confidence: 99%

Sound attenuation optimization using metaporous materials tuned on exceptional points

Xiong¹,

Nennig²,

Aurégan³

et al. 2017

The Journal of the Acoustical Society of America

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“…The maximum attenuation is found for an impedance leading to the coalescence of two or more modes. 1 However, the determination of all different modes is generally difficult. As quoted in Astley et al, 2 "The evaluation of the eigenvectors even for ducts of separable geometry, is a nontrivial exercise, particularly when flow is present.…”

Section: Introductionmentioning

confidence: 99%

Calculations of modes in circumferentially nonuniform lined ducts

2008

The Journal of the Acoustical Society of America

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This paper proposes a computationally efficient method of determining eigenfunctions and eigenvalues of acoustic modes propagating in circular lined ducts with zero or uniform flow. Linings with circumferentially nonuniform impedance, as found in nacelle acoustics, are the focus. The method of solution adapts in two important respects--the presence of flow and the imposition of impedance boundary conditions--the series expansion method first proposed by Pagneux et al. [J. Acoust. Soc. Am. 110, 1307-1314 (2001)] to calculate the eigenvalues of Lamb modes. The inclusion of flow, and a corresponding different method of solution leading to an improved convergence of eigenvalues (O(N(-5)), N is the truncation of radial basis of expansion), is the important new feature as compared to the previous adaptation by Bi et al. [J. Acoust. Soc. Am. 122, 280-291 (2007)]. As a result, it becomes possible to safely determine and in a simple manner the eigenvalues and eigenfunctions of circumferentially nonuniform lined ducts in the presence of uniform flow, up to relatively high frequencies (e.g., 30

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“…Although a straight duct with uniform velocity profile and impedance wall is a simplification, it is an important model of the lined duct of a real turbofan engine [1][2][3][4][5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

A classification of duct modes based on surface waves

2003

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For the relatively high frequencies relevant in a turbofan engine duct, the modes of a lined section may be classified in two categories: genuine acoustic 3D duct modes resulting from the finiteness of the duct geometry, and 2D surface waves that exist only near the wall surface in a way essentially independent of the rest of the duct. Per frequency and circumferential order there are at most four surface waves. They occur in two kinds: two acoustic surface waves that exist with and without mean flow, and two hydrodynamic surface waves that exist only with mean flow. The number and location of the surface waves depends on the wall impedance Z and mean flow Mach number. When Z is varied, an acoustic mode may change via small transition zones into a surface waves and vice versa.Compared to the acoustic modes, the surface waves behave-for example as a function of the wall impedance-rather differently as they have their own dynamics. They are therefore more difficult to find. A method is described to trace all modes by continuation in Z from the hard-wall values, by starting in an area of the complex Z-plane without surface waves.

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The optimization of modal sound attenuation in ducts, in the absence of mean flow

Cited by 114 publications

References 7 publications

Sound attenuation optimization using metaporous materials tuned on exceptional points

Sound attenuation optimization using metaporous materials tuned on exceptional points

Calculations of modes in circumferentially nonuniform lined ducts

A classification of duct modes based on surface waves

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